1. Field of the Invention
The present invention relates to an MRI (magnetic resonance imaging) apparatus and a magnetic resonance imaging method which excites nuclear spin of an object magnetically with an RF (radio frequency) signal having the Larmor frequency and reconstructs an image based on an NMR (nuclear magnetic resonance) signal generated due to the excitation, and more particularly, to a magnetic resonance imaging apparatus and a magnetic resonance imaging method which allows an operator to set an imaging condition for applying a single or plural pre-pulses easily.
2. Description of the Related Art
MRI is an imaging method which excites nuclear spin of an object set in a static magnetic field with an RF signal having the Larmor frequency magnetically and reconstructs an image based on an NMR signal generated due to the excitation. That is, echo signals with regard to spins included in an imaging region of an object are acquired and an MRI image is generated based on the acquired echo signals.
In an ordinary MRI, plural pre-pulses are applied prior to an application of an excitation pulse for acquisition of an NMR signal. Types of pre-pulses include a SORS (slice-selective off-resonance sinc pulse), a presat (presaturation) pulse, a t-SLIP (time-Spatial Labeling Inversion Pulse), a MTC (magnetization transfer contrast) pulse and so on. For example, in the t-SLIP method, a tagging inversion pulse is applied with a slice selective excitation gradient magnetic field pulse subsequently to inversion of a spin in an imaging region by an inversion pulse. Consequently, the spin of a tag region selected regionally is inverted and tagged (see, for example, Japanese Patent Application (Laid-Open) No. 2001-252263). A presat pulse is applied for suppressing a flow artifact, vein signals or effects of motion and vibration, there is the case that a presat pulse is applied plural times.
Therefore, when an imaging condition is set, an operator needs to set a type and an order of one or more pre-pulses to be applied in addition to an imaging selection.
FIG. 1 is a diagram showing an example of conventional screen for setting a pre-pulse.
As shown in FIG. 1, a section is set every pre-pulse since there is the case that a section excited by a pre-pulse is set separately from an imaging section. That is, a LOCATOR IMAGE 2 for setting an excitation section is displayed on a monitor 1. Then, a slice SO2 excited as an imaging section is set. A slice SO1 excited by an ASL (Arterial spin labeling) PULSE which is a pre-pulse for tagging a blood flow flowing into the imaging section is set. In addition, slices SO3 and SO4 excited by two pre-pulses (SATBAND PULSE 1, SATBAND PULSE 2) for signal suppression are set.
Further, when water selective excitation pulse or a fat saturation pulse is applied as a pre-pulse, water excitation or fat saturation is performed by matching a center frequency of the pre-pulse a resonant frequency of signals from a water region such as blood (water signals) or signals from a fat region (fat signals).
However, on a conventional screen for setting a pre-pulse, a slice excited by each pre-pulse is displayed only as just a box as shown in FIG. 1. Therefore, it may be hard for an operator to see the relation between a pre-pulse and a slice. That is, it is hard for an operator to see at which slice position and in which order each pre-pulse is applied easily. Specifically, when a presat pulse and a t-SLIP are applied or when plural presat pulses are applied, to see time-series information is hard.
Further, when a water selective excitation pulse or a fat saturation pulse is applied as a pre-pulse, it is necessary to match a center frequency of the pre-pulse with a resonant frequency of water signals or fat signals. However, there is a problem in that it becomes difficult for an operator to set the center frequency of the water selective excitation pulse or the fat saturation pulse since a peak of the water signals or the fat signals on a frequency spectrum spreads depending on a part to be imaged in an object or a shape of an imaging target.
For this reason, it is preferable to create an interface with improved operability so that an operator can set single or plural pre-pulses for various objects such as water excitation or fat saturation easily.